As the demand for new wireless communication services and systems continues to expand, appropriate unused frequency spectrum for these new wireless systems becomes more difficult to identify. Meanwhile, in many situations it is the case that spectrum that has been previously allocated to existing services and systems actually is unused for extending periods of time in some geographical areas. Accordingly, it has become common to repurpose previously allocated frequency spectrum for new wireless communication services and systems.
However, in general when new wireless devices are permitted to operate in previously-allocated frequency bands, there is a requirement for these new wireless devices to protect the incumbent users of these frequency bands from interference. One example of this situation is presented by the development of wireless communication devices operating according to WiMedia ultrawideband (UWB) communication protocols.
In particular, detection and avoidance (DAA) is mandatory in Europe and Japan for UWB wireless devices operating in frequency spectrum from 3-4 GHz in order to satisfy regulatory requirements in those countries. The main purpose of DAA is to enable UWB devices to detect nearby incumbent devices operating in this frequency spectrum, and then adopt appropriate measures to protect the incumbent devices from potential interference caused by the UWB wireless devices and vice versa.
In particular, incumbent wireless devices that operate according to the emerging, worldwide WiMAX communication protocol may be affected by interference from UWB wireless devices. In a WiMAX network, a so-called WiMAX subscriber unit cannot transmit an “uplink” signal until it first receives a “downlink” signal from a WiMAX base station. If a WiMAX subscriber unit is located near one or more UWB wireless devices with heavy data traffic, and/or on the fringe of the coverage area of a WiMAX base station, then the WiMAX subscriber unit may not be able to receive the WiMAX base station's signal. In that case, the WiMAX subscriber unit cannot initiate an uplink transmission. Without an uplink transmission from the WiMAX subscriber unit, any nearby UWB wireless devices will not be able to detect the WiMax subscriber to avoid interfering with it. So this becomes a circular problem.
One solution to this problem is to insert silent periods in the transmissions of UWB wireless devices, so that any nearby WiMAX subscriber will at least have some opportunity during the silent periods to detect a downlink signal from a WiMAX base station and respond with an uplink signal to establish a link, which can then be detected by any nearby UWB wireless devices.
FIG. 1 illustrates silent periods in a UWB transmission. FIG. 1 illustrates how in each time period 100, TTOTAL, all UWB devices must remain silent for a time interval 110, TSILENT. Experiments have shown that to minimize the impact of UWB wireless devices on WiMAX subscriber units, and to insure that the WiMAX subscriber units will be able to “hear” a downlink signal from a WiMAX base station and then transmit an uplink signal which can be detected by nearby UWB wireless devices, TSILENT should be about 250˜300 ms and TTOTAL should be about 900 ms.
Unfortunately, a silent period of 250˜300 ms has a severe, negative, impact on the operation of UWB wireless devices. First, a UWB wireless device using the WiMedia communication protocol should not lose more than three consecutive beacons transmitted by a neighbor. Otherwise, according to the current WiMedia specification, the UWB device has to conclude that this neighbor has disappeared. Given that the time interval between two consecutive beacon transmissions from a UWB device is about 65 milliseconds, a silent period of 250˜300 milliseconds, which is four times larger than 65 milliseconds between beacons, will break the normal operation of beacons. In addition, the data transmission also has to be suspended during the silent period, which can easily compromise quality of service (QoS) requirements for some UWB applications.
Accordingly, it would be desirable to provide a wireless communication device and method of wireless communication in a wireless communication system that provides a silent period for detecting the presence of other wireless communication devices operating in other wireless communication systems in the same frequency spectrum, to avoid interference with them. It would be particularly desirable to provide a UWB wireless device and corresponding method of operation that provides a silent period for detecting the presence of nearby WiMAX subscriber units operating in the same frequency spectrum, to avoid interference with them.
In one aspect of the invention, a method is provided for communication by a first wireless device operating according to a first communication protocol in at least a first set of frequency bands, wherein one or more of the frequency bands in the first set overlaps at least a portion of a second set of one or more frequency bands on which a second wireless device operates according to a second communication protocol. The method comprises: (1) dividing a time cycle into a plurality of subcycles, each subcycle having a period long enough for the second wireless device to receive a first signal according to the second communication protocol and to transmit a second signal according to the second communication protocol; (2) in each of the subcycles, selecting one of a plurality of logical channels available to the first wireless device, each logical channel employing a corresponding hopping sequence for frequency hopping among a subset of the frequency bands in the first set; (3) transmitting from the first wireless device a signal according to the first communication protocol in each of the subcycles, using the selected logical channel for that subcycle; and (4) repeating steps (1) to (3) over a plurality of time cycles. In each time cycle, each of the frequency bands of the first set which overlaps at least a portion of the second set of frequency bands is excluded in at least one of the hopping sequences employed by at least one of the logical channels selected in at least one of the subcycles.
In another aspect of the invention, a first wireless device is adapted to communicate according to a first communication protocol in at least a first set of frequency bands, wherein one or more of the frequency bands in the first set overlaps at least a portion of a second set of one or more frequency bands on which a second wireless device communicates according to a second communication protocol. The first wireless device comprises: a receiver; a transmitter; and at least one antenna operatively connected to the wireless receiver and wireless transmitter. The wireless device: (1) divides a time cycle into a plurality of subcycles, each subcycle having a period long enough for the second wireless device to receive a first signal according to the second communication protocol and to transmit a second signal according to the second communication protocol; (2) in each of the subcycles, selects one of a plurality of logical channels available to the first wireless device, each logical channel employing a corresponding hopping sequence for frequency hopping among a subset of the frequency bands in the first set; (3) transmits a signal according to the first communication protocol in each of the subcycles, using the selected logical channel for that subcycle; and (4) repeats steps (1) to (3) over a plurality of time cycles. In each time cycle, each of the frequency bands of the first set which overlaps at least a portion of the second set of frequency bands is excluded in at least one of the hopping sequences employed by at least one of the logical channels selected in at least one of the subcycles.